Choi shot a 5-under-par 67 to take sole possession of the lead.
Playing more than half her round in a steady afternoon rain, Choi, 22, avoided Locust Hill’s gnarly rough off the tee in positioning herself early for her first LPGA title. She hit all 14 fairways.
“My goal was just hit fairways,” said Choi, who is in her fifth LPGA season. “So, I’m very happy.”
Choi led going into the final round of the Mobile Bay LPGA Classic last month and ended up tying for fourth.
Choi joked that her failure to win Mobile Bay delayed her father’s retirement. Her father, Ji Yeon Choi, a former South Korean policeman, started caddying for Choi six years ago.
“My father tells me he wants to retire after every tournament,” Choi said. “But I want my father to be on my bag for my first win.”
Pressel closed her morning round with four consecutive birdies to shoot 68 and sits one shot behind Choi. Jiyai Shin also shot 68 in the afternoon rain.
The LPGA’s plan is to play the second round Saturday with a 36-hole finish on Sunday.